In recent years, ink jet printing has progressed by the development of high-performance ink jet printers and by the improvement in inks and the like, and has been widely used in home and for commercial printing. Incidentally, in gravure printing, various works are necessary with respect to gravure rolls, such as manufacture of printing cylinder, change of the cylinder upon patterns change, cleaning, maintenance and so on. Ink jet printing is carried out with each color, i.e. by one color/head, and multi-color printing can be done easily by using plural heads. However, since printing is carried out by moving the heads along the pattern, printing speed is slow. Therefore, it is evaluated to be suitable for a small number of lots, compared with gravure printing which is applicable to a large number of lots.
Recently, the continuous ink jet system was developed and gradually utilized where very minute ink drops are produced by a spray nozzle, and fall continuously. Unnecessary ink drops are charged and recovered by an electrode, and only necessary ink drops fall and land to form patterns to achieve printing. According to this system, since the spray nozzle is not necessary to be opened and closed, there is no fear of clogging. Moreover, since the nozzle is fixed and works continuously, printing speed can be raised greatly, compared with conventional ink jet systems, and it is possible that the printing speed is made 120-180 m/min like the gravure printing. Accordingly, it can be considered that the continuous ink jet system is substituted for conventional gravure printing which was employed upon providing multi-color print on a plastic film.
In addition, inks for the ink jet are recently being changed from oily ink to aqueous ink due to the problems of bad smell, working atmosphere, residual solvent odor and reduction of CO2 against global warming, etc. (For example, see Patent Documents 1-4).